Norio Ota

Fabrication of L-shaped Fe4N ferromagnetic narrow wires and position control of magnetic domain wall with magnetic field

We grow a 15-nm-thick ferromagnetic Fe4N epitaxial film on a SrTiO3(001) substrate by molecular beam epitaxy, and process it into approximately 0.5-µm-wide and 24-µm-long L-shaped ferromagnetic narrow wires by electron-beam lithography and Cl2 reactive ion etching. Their longitudinal directions are set in parallel to the magnetic easy axes, Fe4N[100] and [010]. With applying external magnetic field in the direction parallel to Fe4N[100] or [010], the position of domain wall is controlled either on the upper side or lower side of the corner. This experiment is the preliminary step toward current-driven domain wall motion in Fe4N having a negative spin polarization.

Magnetization and spin-polarized conductance of asymmetrically hydrogenated graphene nanoribbons: significance of sigma bands

The magnetization and spin transport of asymmetric zigzag-edge graphene nanoribbons, terminated by hydrogen on one edge while unterminated on the other edge, were investigated by a combination of first-principles calculations and a tight-binding approach. At the unterminated edge, a spin-polarized σ edge state of minority spin appears near the Fermi level and contributes to spin transport. This state enters the band gap for ribbon widths of less than 15 chains, dominating the spin-polarized current. This indicates the importance of the σ edge states in the design of spintronic devices using graphene nanoribbons. We also examined the case where the ‘unterminated’ edge is partially terminated by hydrogen.

Magnetic domain walls in nanostrips of single-crystalline Fe4N(001) thin films with fourfold in-plane magnetic anisotropy

We investigated head-to-head domain walls in nanostrips of epitaxial

Control of domain wall position in L-shaped Fe 4 N negatively spin polarized ferromagnetic nanowire

mathrm{Fe}_4mathrm{N}(001)

Shape effects of GeSbTe nanodots on the near-field interaction with a silver triangle antenna

thin films, displaying a fourfold magnetic anisotropy. Magnetic force microscopy and micromagnetic simulations show that the domain walls have specific properties, compared to soft magnetic materials. In particular, strips aligned along a hard axis of magnetization are wrapped by partial flux-closure concertina domains below a critical width, while progressively transforming to zigzag walls for wider strips. Transverse walls are favored upon initial application of a magnetic field transverse to the strip, while transformation to a vortex walls is favored upon motion under a longitudinal magnetic field. In all cases the magnetization texture of such fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may give rise to peculiar spin-transfer features.

Multiple Spin State Analysis of Magnetic Nano Graphene

Current-driven magnetic domain wall (DW) motion has been extensively studied not only theoretically, but also experimentally. The DW motion is induced by spin-transfer torque, that is, the transfer of spin angular momentum from conduction electrons to localized electrons. The velocity of DW motion is proportional to the spin polarization [P_a = (σ_↑ - σ_↓)/(σ_↑ + σ_↓)] of electrical conductivity (σ) and its direction is the same as electron current when P_σ > 0. The reverse DW motion is thus expected in ferromagnetic materials with negative spin polarization (P_σ <; 0) compared to those with positive spin polarization, because minority spin dominates the electrical conduction. Thereby, spintronics devices composed of both a positive P_σ material and a negative P_σ material, are of fundamental interest. We have paid a lot of attention to ferromagnetic Fe₄N epitaxial films for application to spintronics devices because it is theoretically expected to have a large negative spin polarization (P_σ = -1.0). Very recently, we confirmed its negative spin polarization by experiment.

Super-exchange Ferromagnetic Order Analysis of FeO-modified Graphene-nano-ribbon

We investigated the shape effects of GeSbTe nanodots on the near-field interaction with a silver triangle antenna using the three-dimensional finite-difference time-domain method, avoiding the difficulty of detecting near-field signals from a single dot that occurs in current measurements. The surface plasmon resonance of silver strengthens the near-field around nanodots made of GeSbTe, commonly used in phase-change recording. Using GeSbTe spheres and pillar dots with various top plane shapes, we investigated the relationship between the inner electric field concentration of GeSbTe nanodots and the radius of curvature of the corners facing the antenna tip. Reducing the radius of curvature strengthens the inner electric field of the dots, enhancing the near-field difference in intensity for the GeSbTe phase change. GeSbTe diamond pillars with a radius of curvature of 1 nm exhibit a near-field difference in intensity of 28% for the phase change. Using the antenna and the GeSbTe nanodot array, optical write-once recording is realized. The preliminary research in this study is expected to realize future optical disk storage using GeSbTe nanodots with diameters below 10 nm.